It varies, if its a series I like to have relationships and connections worked out prior to releasing the first character.
I also really benefit from visuals, most of the time the face gens are done before I even start writing.

I also keep a notepad where I plan out what it is I want, like I have a written family tree for each ascended member written down so I can direct the story line accurately to what I intend.

It's tricky, I'm not sure how I do it to be honest. I know that's not helpful. I just kinda write, cut down the token count then after where needed. I use ChatGPT to proof read my intros and things too? I really don't know <3